Elements and Chemical Compounds

(a) Disposal
systems shall
incorporate engineered barrier(s) designed to prevent or
substantially delay the movement of water or
radionuclides toward the accessible environment.

(b) In selecting any engineered
barrier(s) for the disposal system, DOE shall evaluate the
benefit and detriment
of engineered barrier alternatives, including but not limited to: cementation, shredding,
supercompaction,
incineration, vitrification, improved waste canisters,
grout and bentonite backfill, melting of metals, alternative
configurations of waste placements in the disposal
system, and alternative
disposal system dimensions. The results
of this evaluation shall be included in any compliance application and
shall be used to justify the selection and rejection of each
engineered barrier evaluated.

(c)(1) In conducting the evaluation of
engineered barrier alternatives, the following shall be
considered, to the extent practicable:

(i) The ability of the engineered barrier to
prevent or substantially delay the movement of water or waste toward
the accessible environment;

(ii) The impact on worker exposure to
radiation both during and after incorporation of engineered
barriers;

(iii) The increased ease or difficulty of removing the waste from the disposal
system;

(iv) The increased or reduced risk of
transporting the waste to the disposal system;

(v) The increased or reduced uncertainty
in compliance
assessment;

(vi) Public comments requesting specific
engineered barriers;

(vii) The increased or reduced total
system costs;

(viii) The impact, if any, on other waste
disposal programs from
the incorporation of engineered barriers (e.g., the extent to
which the incorporation of engineered barriers affects the
volume of waste);

(ix) The effects on mitigating the consequences
of human intrusion.

(2) If, after consideration of one or
more of the factors in
paragraph (c)(1) of this section, DOE concludes that an
engineered barrier considered within the scope of the evaluation
should be rejected without evaluating the remaining factors in paragraph
(c)(1) of this section, then any compliance application shall
provide a justification for this rejection
explaining why the evaluation of the remaining factors would not
alter the conclusion.

(d) In considering the ability of engineered barriers to
prevent or substantially delay the movement of water or
radionuclides toward the accessible environment, the benefit and
detriment of engineered
barriers for existing waste already packaged, existing waste not
yet packaged, existing waste in need of repackaging, and
to-be-generated waste shall be considered separately and
described.

(e) The
evaluation described in paragraphs (b), (c) and (d) of this
section shall consider engineered barriers alone and in combination.

Assurance requirements are included in the
disposal standard to provide the confidence needed for long-term
compliance with the requirements of 40 CFR
§ 191.13 (U.S. Environmental Protection Agency
1993). 40 CFR § 194.44 (U.S.
Environmental Protection Agency 1996) is one of the six assurance
requirements in the
Compliance
Criteria. Section 194.44 implements the assurance
requirement of 40 CFR § 191.14(d) (U.S.
Environmental Protection Agency 1993) to incorporate one or more engineered barriers at
radioactive waste disposal facilities. The
disposal regulations at 40 CFR
§ 191.12(d) define a barrier as “any
material or structure
that prevents or substantially delays movement of water or
radionuclides toward the accessible environment.” Section 194.44
requires the U.S. Department of Energy (DOE) to
conduct a study of available options for engineered barriers at
the Waste Isolation
Pilot Plant (WIPP) and
submit this study and
evidence of its use with the compliance application.
Consistent with the containment requirement at section 191.13, the
DOE analyzed the performance of the complete disposal system, including the engineered
barrier(s).

The DOE specified the proposed method of incorporating the
engineered barrier (MgO backfill) into the disposal system in the CCA, Chapter 3.0, Section 3.3.3 and Appendix BACK. The DOE
identified MgO as an
engineered barrier and provided the rationale for selecting the
physical form of MgO to
be used, the approximate grain size of the MgO to
be emplaced, and the
type and size of packages to be used to transport and emplace the MgO. The
CCA also described how the MgO minisacks and supersacks would
be arranged around waste containers in the disposal rooms and stated that the MgO
backfill could be emplaced in the same manner and with the same equipment as the waste
containers.

The EPA found that the DOE conducted the
requisite analysis of engineered barriers and selected an
engineered barrier designed to prevent or substantially delay the
movement of water or
radionuclides toward the accessible environment. In the 1998
Certification Decision (U.S. Environmental Protection Agency 1998), the EPA specified
that only the MgO backfill met the regulatory definition
of an engineered barrier. The EPA determined that the DOE provided
sufficient documentation to show that MgO
can effectively reduce
actinide (An) solubility in the disposal system.

A complete description of the
EPA’s 1998 Certification Decision for section 194.44 can be found in U.S. Environmental Protection
Agency 1998.

In the CRA-2004, the DOE did not report any
significant changes to the information on which the EPA based
the 1998 Certification Decision. The DOE submitted two
planned change requests and one planned change notice after the
original certification decision. The DOE’s requests
included a request to eliminate the MgO minisacks, the
notification of a new MgO vendor, and a request to emplace
compressed waste from Idaho National Laboratory (INL; formerly
Idaho National Engineering and Environmental Laboratory).
These changes were approved by the EPA prior to the 2004
submission of the Compliance Recertification Application
(CRA-2004, U.S. Department of Energy 2004). Details of these
submissions are documented in Section
44.5. These changes are discussed in detail in Appendix
MgO-2009 (see Section
MgO-2.1.2 for the minisack elimination change, Section
MgO-2.2 for the vendor change, and Section
MgO-2.1.3 for the compressed waste change).

Since the final engineered barrier was selected
by the DOE using the results of the section
194.44 analysis in the CCA, Appendix EBS,
the DOE did not conduct a new analysis to evaluate the benefit
and detriment of
engineered alternatives (originally required by 40 CFR
§§ 194.44(b) through (e)). The CRA-2004 reflected
the EPA’s determination that only the MgO
backfill met the
EPA’s requirements for an engineered
barrier.

The EPA did not identify any significant changes
in the implementation of the requirement for engineered barriers
based on their review of the activities and conditions in and
around the WIPP
site. The CRA-2004 did not reflect any changes to the
analysis of engineered barrier documented in the CCA, Appendix EBS. The CRA-2004 accurately reflected the 1998
Certification Decision and its conclusion that the MgO backfill
is the only engineered barrier that met the EPA’s
requirements (U.S. Environmental Protection Agency 1998).

There are no significant changes in the factors
on which the EPA based the determination of compliance with section 194.44. The DOE did not
change the engineered barrier type, form, or function and
therefore did not conduct a new analysis to evaluate the benefit
and detriment of
engineered alternatives (originally required by sections
194.44(b) through (e)). The CRA-2009 follows the
EPA’s determination that only the MgO
backfill met the
EPA’s requirements for an engineered
barrier at section 191.14(d).

The DOE had proposed shaft seals, borehole plugs,
and panel closures as engineered barriers in the CCA.
Changes to the approved engineered barrier that have occurred
since the last recertification and changes to other disposal
system design features originally proposed as engineered barriers
(termed disposal system barriers) will be discussed in the
following subsections for completeness.

MgO is used in the WIPP to meet the requirements
for multiple natural and engineered barriers. MgO acts as
an engineered barrier by decreasing An solubilities through the
consumption of essentially all carbon dioxide (CO2)
possibly produced by microbial activity. Since microbial
activity is an uncertain process, the MgO engineered barrier
reduces uncertainty in the repository chemical conditions by
ensuring low CO2 fugacity and by controlling pH (see
Appendix
MgO-2009, Section MgO-5.0 and Appendix
SOTERM-2009, Section SOTERM-2.3).

The description of the supersacks and their
placement in the disposal system is described in the CRA-2004, Chapter 3.0, Section 3.3.1. Minor emplacement changes
were made as a result of an EPA-approved planned change for
disposal of compressed waste (Marcinowski 2004). This change was approved prior to
the submittal of the CRA-2004, but was not described in that
application. This change will be discussed in Section 44.6.1.2. The representation
of the engineered barrier in performance assessment (PA) is
described in the CRA-2004, Chapter 6.0, Section 6.4.6.4 (with minor editing in response
to the EPA Comment C-23-5 [Detwiler 2004]), and Appendix PA-2009, Appendix MgO-2009 and
Appendix
SOTERM-2009. The edits correct the stated MgO excess
factor to the EPA-approved 1.67 value. A detailed history
of the MgO engineered barrier is presented in Appendix MgO-2009
and describes the placement, function, and experimental
activities associated with the barrier since it was first
proposed. This document (Appendix MgO-2009) describes in
greater detail the changes that have occurred since the
CRA-2004.

The developments associated with the MgO
engineered barrier that have occurred since the EPA’s
Recertification Decision include information from additional
analyses and the DOE’s planned change requests. These
developments include the following:

1.
A change in MgO vendor

2.
The EPA’s approval of the DOE’s planned change
request to dispose of compressed waste

3.
The EPA’s approval of the DOE’s planned change
request to change the MgO excess factor from 1.67 to 1.20

National Magnesia Chemicals of Moss Landing, CA,
was the first vendor to provide MgO for the WIPP. National
Magnesia supplied MgO from the opening of the WIPP in
March 1999 (Panel 1, Room 7) through mid-April 2000, at
which time National Magnesia stopped producing MgO. Based
on cost and the results of a technical evaluation, the DOE
selected Premier Chemicals of Gabbs, NV, as the MgO supplier (see
Section 44.5, above). Premier Chemicals
supplied MgO from mid-April 2000 (Panel 1, Room 7) through 2004
(Panel 2, Room 2). In 2004, Premier Chemicals informed WTS
that it would soon be unable to provide MgO that met the
requirement for the minimum concentration of MgO in the
DOE’s specification (Washington TRU Solutions [WTS] 2003). The DOE selected
Martin Marietta Magnesia Specialties LLC, which has supplied the
MgO emplaced since January 2005 (Panel 2, Room 2). The DOE
selected Martin Marietta’s MgO based on cost and a
technical evaluation of its suitability by Wall (2005). The results of this study and additional
characterization of Martin Marietta’s MgO are described in
more detail in Appendix
MgO-2009, Section MgO-4.3.

In March 2004, the EPA approved the emplacement
in the WIPP of compressed (supercompacted) waste from the
Advanced Mixed Waste Treatment Project (AMWTP) at the INL (Marcinowski 2004, Trinity Engineering Associates 2004, U.S. Environmental Protection Agency 2004). However,
the EPA specified that the DOE must maintain an MgO excess
factor (see Section 44.5) of 1.67. The
AMWTP waste contains concentrations of CPR materials that are
higher than the average concentration of CPR materials in
transuranic (TRU) waste, necessitating the emplacement of
additional MgO. Therefore, in addition to the one supersack
per stack configuration, the DOE has emplaced additional MgO
supersacks on racks placed among the waste containers.
These additional supersacks are emplaced as required to meet the
excess factor. Each rack contains five supersacks identical
to those placed on top of the waste containers, and spans the
same vertical distance normally occupied by three 7-packs
of 55-gallon (208-liter) drums, 3 Standard Waste Boxes, or
various combinations of these and other waste containers.
Thus, emplacement of additional MgO in the repository has used
space normally occupied by contact-handled (CH) transuranic (TRU)
(CH-TRU) waste.

In April 2006, the DOE requested that the EPA
approve a reduction in the MgO excess factor from 1.67 to 1.2 (Moody 2006a). To justify its request, the DOE used
reasoned arguments regarding health-related transportation risks
to the public, the cost of emplacing MgO, and the uncertainties
inherent in predicting the extent of microbial consumption of CPR
materials during the 10,000-year WIPP regulatory period.
The EPA responded by requesting that the DOE address the
uncertainties related to MgO effectiveness, the size of the
uncertainties, and the potential impact of the uncertainties on
long-term performance. In particular, the EPA instructed
the DOE to (1) identify all uncertainties related to the
calculation of the MgO excess factor, and (2) quantify these
uncertainties, if possible (Gitlin 2006). The DOE responded to this request with a
detailed uncertainty analysis (Moody 2006b). In February 2008, the EPA approved the
reduction of the MgO excess factor to 1.2 (Reyes 2008, Langmuir 2007, Cohen and Associates 2008, U.S. Environmental Protection Agency 2008).

MgO investigations include characterization of
the current vendor’s (Martin Marietta) MgO, hydration and
carbonation experimental updates, and independent reviews of the
use of MgO as an engineered barrier at the WIPP. Deng et
al. (2006) and Deng, Xiong, and Nemer (2007) investigated the characteristics and properties of a
sample of Martin-Marietta-supplied MgO identical to that emplaced
in the WIPP. The analysis looked at the particle size and
morphology; the weight percentage of magnesium, calcium,
aluminum, iron, and silica of the sample; and the loss on
ignition and gravimetric analysis of hydrated MgO. The
investigation also included a qualitative analysis using scanning
electron microscope imaging and the associated energy dispersive
spectrum of the as-received MgO. The results of these
investigations helped to confirm that the MgO backfill will
perform as expected in the WIPP environment (see Appendix
MgO-2009, Section MgO-3.0 and Section
MgO-4.0, for a summary of these investigations and their
results).

The following sections discuss changes to other
disposal system design features that were also proposed as
engineered barriers in the CCA: shaft seals, panel closures, and
borehole plugs. While shaft seals, panel closures, and
borehole plugs are not considered engineered barriers by the EPA,
they are important physical elements of the WIPP disposal
system. It is within this context that they are discussed
below.

The DOE submitted a planned change request to
modify the panel closure design in 2002, prior to submittal of
the CRA-2004 (Triay 2002). Because the EPA determined the change
would require a rulemaking, they deferred their review until
after the certification decision (Marcinowski 2002). In January 2007, the DOE renewed
their request for EPA approval of the 2002 panel closure planned
change request (Moody 2007a). This letter also requested a delay in
permanent closure of panels to allow gas monitoring, through a
substantial barrier, with the installation of the permanent
closure depending on the results of the monitoring. The
proposed monitoring was intended to develop an understanding of
flammable gas generation rates in filled panels of waste in order
to optimize the final panel closure design. The DOE also
requested that the EPA modify Condition 1 of the original
certification decision to acknowledge that the New Mexico Environment Department
(NMED) is responsible for regulating the design and
construction of the panel closure system, provided that the DOE
demonstrates there are no long-term impacts on performance.
In their letter, the DOE provided a detailed justification for
this request and stated that the closure is an operational period
requirement (Moody 2007a). The purpose of the closure
system is to control volatile organic compound emissions during
operations and protect the health and safety of the
workers. The EPA responded in a subsequent letter agreeing
with the request to delay closure for gas monitoring, but denying
the request to modify Condition 1 of the certification decision
(Reyes 2007). The EPA stated that the panel closure
design was a condition of the EPA’s 1998 certification
decision and that a change in the design is a significant
departure from the most recent compliance application. The
EPA also stated that under 40 CFR
§194.65, the EPA is required to address changes to the
panel closure design through a formal rulemaking process (Reyes
2007). Following a June 2007 panel closure meeting between
the NMED, the EPA, and the DOE, the DOE withdrew the request to
modify the panel closure design pending results of the gas
monitoring and development of a final closure design (Moody 2007b). Option D continues to be the WIPP
baseline panel closure design.

Over the life of the WIPP project, many
exploratory, monitoring, and characterization-related boreholes
have been drilled by the DOE and its predecessors in the vicinity
of the WIPP. In addition to the DOE-drilled wells, water
wells have been drilled for livestock and homesteads, and wells
have been drilled by oil, gas, and potash companies in their
efforts to exploit resources in the Delaware basin. Figure 44-1identifies existing
unplugged boreholes that lie within the WIPP site boundary.
Of these boreholes, two are deep boreholes that exceed the depth
of the repository (WIPP-13 and ERDA-9), and the remainder are
shallow boreholes that do not reach the repository horizon.
There were two additional boreholes deeper than the repository
that have been plugged (DOE-1 and WIPP-12).

To mitigate the potential for contaminants to
migrate toward the accessible environment, the DOE uses
established borehole plugging practices (Christensen and Peterson 1981) to limit the volume of water
that could be introduced to the repository from the overlying
water-bearing zones, and to limit the hypothetical volume of
contaminated brine released from the repository to the accessible
environment. The governing regulations for plugging and/or
abandonment of boreholes are summarized in Table 44-1.

The CRA-2009 monitoring period was from 10/1/2002
through 9/30/2007. Appendix
DATA-2009, Attachment A lists the operational monitoring
wells within the WIPP vicinity. During the monitoring
period, 19 new wells were drilled and put into service: 3
were for the shallow water program and 16 were for the
groundwater program. The shallow water wells were all less
than 23.5 meters (m) (77 feet [ft]) in depth. The
groundwater-monitoring wells varied from 68.3 m to 414.5 m (224
to 1,360 ft) in depth. There were 16
groundwater-monitoring wells plugged during the monitoring
period, and all were plugged solid with cement. During this
monitoring period, two monitoring wells were plugged back,
converted to water wells, and turned over to local ranchers for
their use. In addition, one former potash borehole was
converted to a groundwater-monitoring well. See Appendix
DATA-2009, Attachment A for a description of the wells in the
WIPP monitoring system.

Four deep wells (greater than 655.3 m [2,150 ft]
in depth), DOE 1, ERDA 9, WIPP 12, and WIPP 13 are required to be
plugged in accordance with the State of New Mexico, Oil
Conservation Division, Order No. R-111-P. The key
provisions of Order No. R-111-P are as follows:

·
A salt protection string of casing must be installed at least 100
ft (30 m) below and not more than 600 ft (183 m) below the base
of the salt section. Cementing requirements for both
shallow wells (above 5,000 ft [1,524 m]) and deep wells (below
5,000 ft [1,524 m]) above or below the Delaware Mountain Group
are specified.

·
All oil and gas wells drilled within the potash area must provide
a solid cement plug through the salt section and any water
bearing horizon and prevent liquids or gases from entering the
hole above or below the salt section.

(b) Surface boreholes for development or
holes for prospecting shall be abandoned to the satisfaction of
the authorizing officer by cementing and/or casing or by other
methods approved in advance by the authorized officer. The
holes shall also be abandoned in a manner to protect the surface
and not endanger any present or future underground operation, any
deposit of oil, gas, or other mineral substances, or any
aquifer.

In the event that the test or exploratory
well is to be abandoned, the state engineer shall be
notified. Such wells shall be plugged in accordance with
Article 4-19.1 so that the fluids will be permanently confined to
the specific strata in which they were originally
encountered.

(1) Before an
operator abandons a well, the operator shall plug the well in a
manner that permanently confines all oil, gas and water in the
separate strata in which they are originally found. The
operator may accomplish this by using mud-laden fluid, cement and
plugs singly or in combination as approved by the division on the
notice of intention to plug.

(2) The
operator shall mark the exact location of plugged and abandoned
wells with a steel marker not less than 10.2 centimeters
(4 inches) in diameter set in cement and extending at least
1.2 m (4 ft) above mean ground level. The operator name,
lease name and well number and location, including unit letter,
section, township and range, shall be welded, stamped or
otherwise permanently engraved into the marker’s metal.

(1) All
existing and future wells that are drilled within the potash area
shall be plugged in accordance with the general rules established
by the Division. A solid cement plug shall be provided
through the salt section and any water-bearing horizon to prevent
liquids or gases from entering the hole above or below the salt
selection.

It shall have
suitable proportions—but no greater than three percent of
calcium chloride by weight—of cement considered to be the
desired mixture when possible.

·
The fluid used to mix the (plugging) cement must be saturated
with salts common to the salt section penetrated, but not more
than 3% of calcium chloride by weight of cement wherever
possible.

Two of the four deep wells (WIPP-12 and DOE-1)
were plugged and abandoned. The New Mexico Office of the
State Engineer (OSE) regulates the drilling, operation, and
abandonment of groundwater wells. This agency has
regulatory oversight of wells in the controlled area.
Although WIPP-12 was plugged with standard cement slurry (no
salt), the OSE subsequently agreed that the use of standard
cement slurry was acceptable for this instance. DOE-1 was
plugged using a salt-saturated cement through the salt section,
and a standard cement slurry through the rest of the
borehole.